Mate sampling influences the intensity of sexual selection and the evolution of costly sexual ornaments.

Mate choice includes three steps: (1) a choosing individual encounters potential mates, (2) assesses and processes information about them, and (3) makes a mate decision. During mate searching females can access only a sample of males in the mating pool and need to choose their mates based on limited information. Thus, mate sampling may influence sexual selection promoted by mate choice because it constrains female choice. Using individual-based simulations, we found that both female choosiness and mate sampling influenced the variance in mating success among males and thus the intensity of sexual selection. So that sexual selection is most intense when females are strongly choosy and can sample many males. Moreover, in evolutionary simulations, the rate of evolutionary change and the final size of male ornament increase with increasing mate sampling. However, under stronger natural selection, evolutionary change is slower and leads to smaller ornaments. Empirical data on the potential for sexual selection (Is) for several animal species show a positive correlation between the intensity of sexual selection and an index of mate sampling based on behavioral and ecological traits. Based on the results of our simulations, we predict that males of highly mobile species with long-range sexual signal transmission, which allow females to assess many males, will show greater variance in mating success and will be more ornamented than their relatives not exhibiting these features.

Allometry and morphological trait relationship in the sexually dimorphic Chinese dobsonfly, Acanthacorydalisasiatica (Wood-Mason, 1884) (Megaloptera, Corydalidae).

Male insects with large weapons such as horns and elongate mandibles would be expected to invest more on such structures than other parts of the body for advantages in male to male competition for mating. In male genitalia, however, intermediate size provides a better fit for more females than small or large sizes, and such a male would leave more offspring regardless of their body size. These predictions were tested using a static allometry analysis between body size and other trait sizes. Acanthacorydalisasiatica is a large dobsonfly (Megalotera) and males have conspicuously large mandibles used as weapons. We examined the hypothesis that the male mandibles of this sexually dimorphic species are sexually selected to enlarge, whereas the male genitalia are stable to be intermediate regardless of a great variation in body size. The results, as predicted, showed positive allometry between male body size and mandible length but negative allometry between male body size and ectoproct length (a male grasping structure). Sperm are transferred through a small spermatophore attached externally to the female genital opening, so it may be evolutionarily unnecessary to develop an enlarged male genital size. In contrast, there may be a trade-off between male mandible size and wing length, because of negative allometry between body size and wing length in males but isometry between them in females.